<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            width: 500px;
            height: 500px;
            background-color: #ccc;
            color: #fff;
            text-align: center;
            font-size: 100px
        }
    </style>
</head>
<body>
    <div class="box"></div>
    <script>
        const box = document.querySelector('.box')
        let i = 1 //让这个变量++
        function mouseMove(){
            box.innerHTML = ++i
            //如果里面存在大量操作 dom 的情况下， 可能会卡顿
        }
        //防抖函数
        function debounce(fn, t){
            let timeId
            return function(){
                //如果有定时器就清除
                if(timeId) clearTimeout(timeId)
                //开启定时器 200
                timeId = setTimeout(function(){
                    fn()
                }, t)
            }
        }
        box.addEventListener('mousemove', debounce(mouseMove, 200))
    </script>
</body>
</html>